Datasheet ADN8810 clarification

I need to make a laser driver that can give current output from 0 mA to 250 mA. I checked ADN8810 datasheet and found the recommended circuit with 2 resistors (Rsn) which are having value written over them as 1.6V (instead of ohm/kohm). Is this a typo?

Also I need to ask whether the recommended circuit shown is to get 300mA only or the circuit connection stays the same for smaller current values as well?

  • Dear Rohan09,

    Firstly, sorry about the typo. The Rsn = 1.6ohm should be the correct ones in Fig. 1 of ADN8810 datasheet.

    We have noticed these typos and is working on the datasheet revision to fix these typos.

    Secondly, with the same Fig. 1 circuit configuration, the full scale current could be determined by the equation (1). In the equation two factors: Rsn & Vref would result in the expected full scale current. For example, if you have a Vref = 2.048V, Rsn = 3.7ohm, the resulted full scale current would be about 55.4mA. This leads to LSB (resolution) --> 55.4/4096 = 13.5uA. Or Vref = 4.096V, Rsn = 7.4ohm, you would get the similar full scale current 55.4mA.

    In general, we recommend a 4.096V as the Vref input.

    In case you have any further proprietary questions about ADN8810 application, please feel free to send your questions

    to dongfeng.Zhao@analog.com or continue our open discussion here in EZ.

    Best Regards,

    Dongfeng

  • Thanks Dongfeng for the help,

    I have made the circuit as was in the datasheet and trying to get the output current, but failed. I am adding the circuit connection pdf file.Kindly have a look and let me know if somthing is wrong

    Baud rate =9600

    Bit resolution = 12 bit

    Master : TMS320F28377D

    Slave : ADN8810

  • Dear Rohan,

     

    ADN8810 is target to work with a laser diode, with about a threshold voltage: 1.6 ~ 1.8V. Please refer to datasheet Fig.1.

     

    In your prototype design, you have used one 1kohm resistor to replace the laser diode. At about Iout = 30uA,

    You could only generate 30mV, plus the voltage drop on Rsn, the resulted Vout voltage is still far below from the min. required Vcomp: 2.0V.  This might be the root cause why you failed to make ADN8810 works.

     

    Please replace the 1kohm resistor with one diode load (with a proper threshold voltage) hooked up as Fig.1 recommended, you would see a working ADN8810.

     

    Best Regards,

     

    Dongfeng

  • Hello Dongfeng:

    I tried using your email but it seems it doesn't work so I'll message you here.

    Based from your reply, you mentioned Iout = 30uA. Obviously this wouldn't fulfill the required Vcomp of 2V. But if Rohan chooses, Iout = 2mA, it should fulfill the minimum Vcomp of 2V. Will his circuit now work? I interpret this failure-or-not-failure situation as dependent on how much Iout you program ADN8810 to output.

    Anyway another question. If I will not use SB and RESET, do I just NIC them? connect them to ground? PVDD?

    Thanks